Head/data request in 3D graphics

ABSTRACT

A method for efficiently processing graphics data for graphics primitives, the graphics data including vertex coordinate information and vertex attribute data. Coordinate information, in the form of homogeneous coordinates, of the graphics primitive determines whether the graphics primitive is to be rendered. If the primitive is to be rendered, then attribute data associated with the location information is retrieved. However, if the data is not to be rendered, then the location information is discarded. By only retrieving parameters for a primitive that is rendered, performance is increased. In one embodiment, the attribute data is fetched before it is known whether or not the graphics primitive is to be rendered, and if not, the prefetch is aborted, and new location information is fetched.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to U.S. patent application Ser. No. ______, filed (Atty. Docket No. 21600-302201), entitled HEAD/DATA SCHEDULING IN 3D GRAPHICS, the contents of which are incorporated by reference into the present application.

FIELD OF THE INVENTION

[0002] The present invention generally relates to processing of 3D graphics primitives and more particularly to a system and method for managing a pipeline, in which the graphics primitives are processed, to improve performance.

DESCRIPTION OF THE RELATED ART

[0003] For 3D graphic applications, each vertex has coordinates (X, Y, Z, W), color attributes (specular, ARGB, Diffuse ARGB and fog), and texture parameters (U, V). Referring to Table 1, typical data for triangles is shown. Specifically, triangle 0 has vertex coordinates HT0 and vertex attributes DT0_d (diffuse color), DT0_s (specular color), DT0_f (fog color), DT0_T (texture). Triangles 1 and 2 have the same parameters that is HT1, DT1_d, DT1_S, DT1_f and DT1_t, for triangle 1 and HT2, DT2_d, DT2_s, DT2_f, DT2_t for triangle 2. As seen in Table 1, it takes thirty (30) cycles to process data in the pipeline for six triangles. TABLE 1 Cycle 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Data HT0 DT0_(—) DT0_(—) DT0_(—) DT0_(—) HT1 DT1_(—) DT1_(—) DT1_(—) DT1_(—) HT2 DT2_(—) DT2_(—) DT2_(—) DT2_(—) d s f t d s f t d s f t Cycle 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 HT3 DT3_(—) DT3_(—) DT3_(—) DT3_(—) HT4 DT4_(—) DT4_(—) DT4_(—) DT4_(—) HT5 DT5_(—) DT5_(—) DT5_(—) DT5_(—) d s f t d s f t d s f t

[0004] Also evident from Table 1, when multiple triangles are rendered by a graphics processor, not only the homogeneous coordinates (X, Y, Z, W) but also the vertex attributes must be fetched. As the use of more textures and other parameters increases, increasing amounts of vertex attributes must be fetched. However, statistically, only about half of the triangles are ever rendered on the screen. The other half of the triangles are either rejected as being either outside of the scissors box or by culling. Therefore, there is no need and a waste of processing cycles to fetch the data of the rejected or culled triangles.

[0005] As such, there is a need for a method that reduces the amount of data entered into the pipeline.

BRIEF SUMMARY OF THE INVENTION

[0006] A method in accordance with and embodiment of the present invention includes loading a pipeline with HEAD information for a predetermined number of graphics primitives, and performing a test based on the HEAD information in the pipeline to determine whether or not a graphics primitive is to be rendered, where the test has a latency of a given number of pipeline cycles. While performing the test, DATA information is prefetched into the pipeline for the graphics primitive to avoid empty pipeline cycles during the latency of the test and if the test determines that the graphics primitive is to be rendered, the prefetched DATA information for the primitive is processed.

[0007] Another method of processing graphics data for a stream of graphics primitives includes loading a pipeline with HEAD information for a predetermined number of graphics primitives, and performing a test based on the HEAD information in the pipeline for a graphics primitive to determine whether the graphics primitive is to be rendered, where the test has a latency of a given number of pipeline cycles. While performing the test, DATA information is prefetched into the pipeline for the graphics primitive to avoid empty pipeline cycles during the latency of the test and if, during the prefetching, the test determines that a graphics primitive is not to be rendered, the DATA information prefetching is aborting and HEAD information for one or more additional graphics primitives is fetched as needed taking the latency of the test into account.

[0008] One advantage of the present invention is that by preventing the transferring the data parameters of triangles that are not rendered, the speed of the system increases because better use is made of the pipeline cycles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

[0010]FIG. 1 is flowchart illustrating how data is fetched in accordance with the present invention; and

[0011]FIG. 2 is a block diagram of a system to fetch data in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Referring to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the present invention only, and not for purposes of limiting the same, FIG. 1 is a flowchart illustrating how data parameters for graphics primitives such as triangles not being processed can be rejected or culled prior to transfer on the data pipeline. Graphics primitives of the preferred embodiment of the present invention include triangles, but primitives may also include lines, anti-aliased lines, points, and point sprites. Specifically, in step 100, the HEAD data for n primitives are fetched. The HEAD includes the homogeneous coordinate data (i.e., X, Y, Z, W), but not the vertex attribute information for the graphics primitive. From the HEAD data, in step 102, it is possible to determine whether the triangle should be rejected or culled. Specifically, the coordinates X, Y, Z, W (HEAD data) enable the system to determine if the triangle should be rendered on the screen. If the triangle is not rendered, then it is rejected or culled. However, if the triangle is rendered, then, in step 104, the DATA information (attribute information for each of the vertices of the primitive) is fetched for processing. In step 106, it is determined whether all of the HEAD data for the n primitives has been analyzed. If not, then the process returns to step 102, where the next HEAD data is analyzed to determine whether the triangle should be rejected or culled. If the HEAD data for all n primitives has been analyzed, then the process returns to step 100 where more HEAD data is fetched.

[0013] Referring to Table 2, an example for the flowchart of FIG. 1 is shown. Specifically, in cycles 1 through 6, the HEAD data (HT0-HT5) is fetched first. As will be readily apparent, some processing cycles are required to determine whether the primitives should be rejected or culled. For the example in Table 2, it takes eight cycles to process the HEAD data HT0 to determine whether to process the triangle. This leaves cycles 7 through 9 unused.

[0014] For the example in Table 2, primitives (triangles) 0, 2, 4, 5, 8, and 10 are being culled and rejected. Accordingly, only the data for triangles 1, 3, 6, 7, 9 and 11 needs to be fetched. Therefore, beginning with cycle 10, the data (DT1_d, DT1_S, DT1_f, DT1_t) for triangle 1 is fetched. Next, starting with cycle 14, the data for triangle 3 is fetched. During cycles 18 through 23, the HEAD data for additional triangles is fetched, because triangles 4 and 5 are rejected. Therefore, by separating the HEAD and DATA information, and testing the HEAD information, only the data that needs to be processed is fetched, thereby reducing the number of total cycles needed to process the primitives. TABLE 2 Cycle 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Data HT0 HT1 HT2 HT3 HT4 HT5 Empty Empty Empty DT1_d DT1_s DT1_f DT1_t DT3_d Cycle 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Data DT3_s DT3_f DT3_t HT6 HT7 HT8 HT9 HT10 HT11 Empty Empty Empty DT6_d DT6_s Cycle 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Data DT6_f DT6_t DT7_d DT7_s DT7_f DT7_t DT9_d DT9_s DT9_f DT9_t DT11_d DT11_s DT11_f DT11_t

[0015] Table 3 illustrates prefetching data to fill the empty cycles. Table 3 alters the example in Table 1 by using cycles 7, 8, and 9 to fetch the data for the first triangle before it is known whether the triangle should be rejected or culled. The DATA for triangle 0 is fetched in cycles 7, 8, and 9 before it is known whether triangle 0 should be rejected or culled. If triangle 0 is rejected or culled, then the DATA is discarded. If triangle 0 is not rejected or culled, then the remaining data is retrieved in the remaining cycles (i.e., the remaining attribute information for triangle I is retrieved in cycle 10). Therefore, it is possible to improve performance by using otherwise empty cycles for prefetching triangle data. TABLE 3 Cycle 1 2 3 4 5 6 7 8 9 10 11 12 13 Data HT0 HT1 HT2 HT3 HT4 HT5 DT0_d DT0_s DT0_f DT1_d DT1_s DT1_f DT1_t Rejected Rejected Rejected Cycle 14 15 16 17 18 19 20 21 22 23 24 25 26 Data DT3_d DT3_s DT3_f DT3_t HT6 HT7 HT8 HT9 HT10 HT11 DT6_d DT6_s DT6_f Cycle 27 28 29 30 31 32 33 34 35 36 37 38 39 Data DT6_t DT7_d DT7_s DT7_f DT7_t DT9_d DT9_s DT9_f DT9_t DT11_d DT11_s DT11_f DT11_t

[0016] In addition to the foregoing, it is also possible to dynamically determine whether the triangle should be rejected or culled in order to improve efficiency. Specifically, referring to FIG. 2, a dynamic thread selector 200 efficiently processes the DATA and HEAD information in order to reduce processing cycles. Initially, index information for a graphics primitive is stored in vertex cache decoder/request units 0 through 5, 210 a-f. A scheduling/arbitration and HEAD/DATA fetching block 202 retrieves the graphics primitive index from one of the vertex cache decoder/request units 210 a-f. Once the index has been retrieved, a pointer to the coordinate information for the vertices of the primitive is formed by the decoder/request unit. A data calculation block 204 performs the necessary operations on the vertex coordinate data (accessed from the vertex cache 212 using the pointer) to determine whether the primitive should be rejected or culled. Furthermore, once the data has been retrieved, a round robin selector 206 can write new data into the now empty vertex cache decoder/request unit. A six (6) thread register flag 208 tracks which vertex cache decoder/request units are available to receive new indexes and whether the data calculation block is finished processing the retrieved data.

[0017] The scheduling/arbitration block 202 gives priority to HEAD information over DATA information. Therefore, if the data processing in data calculation block 204 has rejected the coordinate information for a certain graphics primitive such as a triangle, then the scheduling/arbitration block 202 gives priority to loading new HEAD information. Thus, it is possible with the thread selector 200 to efficiently choose either HEAD or DATA information when needed in order to save processing cycles.

[0018] An example of processing DATA and HEAD information with the dynamic thread selector 200 is shown. This example is similar to Tables 2 and 3 where triangles 0, 2, 4, 5, 8, and 10 are to be rejected or culled. As seen in Table 4, because the HEAD information has higher priority over the DATA information, the HEAD data is loaded in an earlier cycle, thereby saving processing cycles. This is shown in cycle 11 where the HEAD information for triangle 6 is loaded before all the DATA information for triangle 1 is completed. The dynamic thread selector 200 loads HEAD information in an efficient manner taking into account the latency of the rejection/culling calculation. Where the latency in the rejection/culling calculation is large (i.e., around 24 cycles), the savings in processing cycles can be large. TABLE 4 Cycle 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Data HT0 HT1 HT2 HT3 HT4 HT5 DT0_d DT0_s DT0_f DT1_(—) HT6 DT1_s HT7 DT1_f HT8 Rejected Rejected Rejected d Cycle 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Data HT9 DT1_t HT10 DT3_d DT3_s DT3_f DT3_t HT11 DT6_d HT12 DT6_s DT6_f HT130 DT6_t HT14

[0019] It will be recognized by those of ordinary skill in the art that by determining whether the primitive should be culled or rejected before fetching the DATA information, the processing of the coordinate information of a primitive is ahead of the processing of the attribute information of a primitive. Accordingly, it is necessary to separately maintain a record of the order of the coordinate information from the order of the attribute information. A method and apparatus maintaining a record of the ordering of such information is described in applicant's co-pending U.S. patent application Ser. No. ______, filed ______ (Atty. Docket No. 21600-302201), entitled HEAD/DATA SCHEDULING IN 3D GRAPHICS, the contents of which are incorporated herein by reference.

[0020] Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein. 

What is claimed is:
 1. A method of processing graphics data for a stream of graphics primitives, comprising: loading a pipeline with HEAD information for a predetermined number of graphics primitives; performing a test based on the HEAD information in the pipeline to determine whether or not a graphics primitive is to be rendered, the test having a latency of a given number of pipeline cycles; while performing the test, prefetching DATA information into the pipeline for the graphics primitive to avoid empty pipeline cycles during the latency of the test; and if the test determines that the graphics primitive is to be rendered, processing the prefetched DATA information for the primitive.
 2. A method as recited in claim 1, wherein the graphics primitive is a triangle.
 3. A method as recited in claim 1, wherein the graphics primitive is a line.
 4. A method as recited in claim 1, wherein the graphics primitive is an anti-aliased line.
 5. A method as recited in claim 1, wherein the graphics primitive is a point.
 6. A method as recited in claim 1, wherein the graphics primitive is a point sprite.
 7. A method as recited in claim 1, wherein the graphics primitive has one or more vertices; wherein the HEAD information includes homogenous coordinates of the vertices of the graphics primitive; and wherein the DATA information includes attribute data for the vertices of the primitive.
 8. A method as recited in claim 7, wherein the vertex attribute data includes texture data.
 9. A method as recited in claim 7, wherein the vertex attribute data includes color data.
 10. A method of processing graphics data for a stream of graphics primitives, comprising: loading a pipeline with HEAD information for a predetermined number of graphics primitives; performing a test based on the HEAD information in the pipeline for a graphics primitive to determine whether the graphics primitive is to be rendered, the test having a latency of a given number of pipeline cycles; while performing the test, prefetching DATA information into the pipeline for the graphics primitive to avoid empty pipeline cycles during the latency of the test; and if, during the prefetching, the test determines that a graphics primitive is not to be rendered, aborting the DATA information prefetching and fetching HEAD information for one or more additional graphics primitives as needed taking the latency of the test into account.
 11. A method as recited in claim 10, wherein the HEAD information includes homogenous coordinates of the vertices of the graphics primitive; and wherein the DATA information includes vertex attribute data.
 12. A method as recited in claim 11, wherein the vertex attribute data includes texture data.
 13. A method as recited in claim 11, wherein the vertex attribute data includes color data.
 14. A method as recited in claim 10, wherein the test determines, based on the HEAD information, whether the graphics primitive is outside the boundaries of a screen space.
 15. A method as recited in claim 10, wherein the test determines, based on the HEAD information, whether the graphics primitive is not visible in a screen space.
 16. A method as recited in claim 10, wherein the graphics primitive is a triangle.
 17. A method as recited in claim 10, wherein the graphics primitive is a line.
 18. A method as recited in claim 10, wherein the graphics primitive is an anti-aliased line.
 19. A method as recited in claim 10, wherein the graphics primitive is a point.
 20. A method as recited in claim 10, wherein the graphics primitive is a point sprite.
 21. A system for dynamically processing graphics primitives, comprising: a plurality of memories, each memory being identified by a thread id and configured to store an index for a graphics primitive; a plurality of decoder/request units, one decoder/request unit connected to each memory, each decoder/request unit for providing a HEAD pointer and a DATA pointer based on an index stored in the memory to which the decoder/request unit is connected; a register for storing a plurality of thread flags, one thread flag for each memory, each thread flag receiving completion or rejection information for a thread and indicating whether or not a memory associated with a thread can accept an index; a round robin selector for receiving index information for a graphics primitive and loading the received index into one of the memories based on the thread flag for the memory; scheduling circuitry for selecting one of the decoder/request units to provide a HEAD pointer and a DATA pointer; a data calculation block, coupled to the scheduling circuitry to receive a selected HEAD pointer from the scheduling circuitry and operative to perform a test that determines from HEAD information, accessed via the HEAD pointer during a latency time, whether or not a graphics primitive is to be rendered or rejected, the data calculation block being coupled to the register and operative to indicate when a data calculation for a thread is completed or whether a thread is rejected.
 22. A system as recited in claim 21, wherein the HEAD information includes homogenous coordinates of the vertices of the graphics primitive; and wherein the DATA information includes vertex attribute data.
 23. A system as recited in claim 22, wherein the vertex attribute data includes texture data.
 24. A system as recited in claim 22, wherein the vertex attribute data includes color data.
 25. A system as recited in claim 21, wherein the test determines, based on the HEAD information, whether the graphics primitive is outside the boundaries of a screen space.
 26. A system as recited in claim 21, wherein the test determines, based on the HEAD information, whether the graphics primitive is not visible in a screen space.
 27. A system as recited in claim 21, wherein the graphics primitive is a triangle.
 28. A system as recited in claim 21, wherein the graphics primitive is a line.
 29. A system as recited in claim 21, wherein the graphics primitive is an anti-aliased line.
 30. A system as recited in claim 21, wherein the graphics primitive is a point.
 31. A system as recited in claim 21, wherein the graphics primitive is a point sprite. 